The right wing Hindu nationalist who swept to power in parliamentary elections, according to official results Friday, is a proud outsider. A self-made man whose father sold tea at a railroad station, his blunt style, poor English, and disdain for social graces have made him as distasteful to India’s traditional ruling class as he is popular elsewhere.

“He is breaking the door down,” says Tavleen Singh, a political columnist. “He is the wrong caste, the wrong class, the wrong everything.”

Mr. Modi, a barrel-chested man with a neatly trimmed white beard and mustache, is the first leader of a provincial state to win India’s top political prize. He campaigned hard on his record of economic success in the western state of Gujarat, promising similar benefits for the rest of the country under his leadership.

“He is a doer … who could galvanize the country,” says Gurcharan Das, a multinational company executive turned author. “He is determined and hungry and he can carry people with his sense of purpose.”

Modi’s image as a strong leader was particularly appealing in the wake of an ineffectual government led by the Congress party, which found it hard to make decisions. “Modi stepped into a leadership vacuum,” says political commentator Neerja Chowdhury.

But the next prime minister’s strongman image has compounded alarm about his political rise among India’s Muslim minority, which makes up 19 percent of the population. Many Muslims worry about Modi’s ties to the RSS, a radical group that envisions India as a sacred nation to which only Hindus truly belong. And they recall that he was Gujarat’s chief minister in 2002, when Hindu rioters massacred 2,000 Muslims.

Suspicions that Modi did not do all he might have done to stem the violence have cast a shadow over his political standing. The United States has refused him a visa since the massacre on the grounds that he bore “responsibility for the performance of state institutions” such as the police. But relations have been slowly improving, and US officials have said whoever won the election would be welcome in the US.

But economic policy, not religion, is likely to prove the defining feature of his leadership, says Siddarth Varadarajan, former editor of The Hindu newspaper. “He is the most trusted choice of Indian big business today,” says Mr. Varadarajan. “That is what he represents.”

During his election campaign, heavily funded by Indian businessmen, Modi promised to welcome investors with “red carpets, not red tape.” He put single-minded emphasis on the need for development and economic growth, and stressed the creation of wealth rather than its distribution through welfare programs, which has been the Congress party’s traditional approach.

His record in Gujarat on this front has been generally good, but Modi’s political style worries critics who value India’s tradition of consensual decisionmaking. “He loves controversy and he courts it,” says Ms. Chowdhury. “It’s his way of getting his message across.”

He is also known as a loner who likes to keep personal control over even minor details of policy, and who delegates little responsibility to his subordinates.

At the same time, he has a reputation for honesty in a country that is drowning in corruption; he and his relatives are known to live simply, which is unusual for Indian political leaders.

“He is very passionate about governance and he looks at it as a mission,” says Rajeev Chandrasekhar, an IT millionaire who is now an independent member of the upper house of parliament. “He strikes you as idealistic to a fault.”

During a presidential-style campaign that put his name and track record high above those of his Bharatiya Janata Party (BJP), Modi tapped into the electorate’s desperation for change after a decade of rule by the Congress party.

“He is a risk, because he is communal,” playing on his religious identity, says Mr. Das, who voted BJP for the first time in his life this year. “But I voted for Modi because he is our best chance” of economic prosperity.

As India turns a page, says one foreign diplomat, “Modi could turn out for the best, or he could turn out for the worst.”